Preset files in Reaper can be used to load and save patches outside of the regular Labs dropdown menu. This can be useful in a number of ways, but in particular is useful for loading Labs when using a screen reader.
Loading an RPL file
1. Click the Plus icon to open the plugin options and select "Import Preset Library"
2. Navigate to the location of the RPL file and select the file based on the plugin type that is loaded and click Open
3. The presets can then be loaded from where it says "No Preset"